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A247395
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The smallest numbers of every class in a classification of positive numbers (see comment).
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6
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1, 2, 4, 10, 26, 50, 122, 170, 290, 362, 530, 842, 962, 1370, 1682, 1850, 2210, 2810, 3482, 3722, 4490, 5042, 5330, 6242, 6890, 7922, 9410, 10202, 10610, 11450, 11882, 12770, 16130, 17162, 18770, 19322, 22202, 22802, 24650, 26570, 27890, 29930, 32042, 32762
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OFFSET
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0,2
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COMMENTS
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Consider a classification of the positive numbers with classes {1}, A000040 (primes), A156759 (n>=2) (preprimes, or preprimes of the first kind), A247393 (preprimes of the second kind), A247394 (preprimes of the third kind), etc.
Then a(0)=1, a(1)=2; for n>=3, a(n) is the smallest number which is a preprime of the (n-1)st kind.
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LINKS
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Indranil Ghosh, Table of n, a(n) for n = 0..1000
Vladimir Shevelev, A classification of the positive integers over primes
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FORMULA
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For n>=3, a(n) = (prime(n-1))^2 + 1.
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MATHEMATICA
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Table[If[n>2, Prime[n - 1]^2 + 1, 2^n], {n, 0, 43}] (* Indranil Ghosh, Mar 08 2017 *)
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PROG
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(PARI) a(n)=if(n>2, (prime(n-1))^2 + 1, 2^n) \\ Charles R Greathouse IV, Sep 17 2014
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CROSSREFS
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Cf. A000040, A156759, A247393, A247394.
Sequence in context: A111564 A007021 A100605 * A183947 A154322 A090031
Adjacent sequences: A247392 A247393 A247394 * A247396 A247397 A247398
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KEYWORD
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nonn,easy
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AUTHOR
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Vladimir Shevelev, Sep 16 2014
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EXTENSIONS
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More terms from Peter J. C. Moses, Sep 16 2014
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STATUS
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approved
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